The present invention relates generally to the field of inkjet printing, and more particularly, to bulk ink supplies for inkjet printing systems.
In many conventional bulk ink supply systems for inkjet printers, the printhead of the inkjet printer is supplied with ink from an ink reservoir remote from the printhead by means of ink tubes or lines. Bulk ink supply systems are characteristically sold in industrial markets, typically for address printing. One such exemplary system is the Hp c6119a bulk ink supply system, which includes an ink reservoir with a snap cap (interconnector) which routes an ink tube to a printhead. The ink reservoir/snap cap/ink tube assembly is sold intact and containing ink, the free end of the ink tube being sealed by a fluid interconnect device. During initial setup of the Hp c6119a, the user connects the ink reservoir/snap cap/ink tube assembly to the printhead by inserting the fluid interconnect into a septum/clip device on the printhead. Once this permanent connection is made, the negative pressure, or back pressure at the printhead nozzles is then primarily determined by the positioning of the ink reservoir in relation to the printhead, not by the spring bag in the printhead.
The fact that the back pressure at the printhead nozzle is primarily determined by the positioning of the ink reservoir can lead to a failure mode. Specifically, if the printhead (nozzle plate) is positioned more than about 25 cm above the reservoir then a de-prime occurs, as the back pressure at the nozzles exceeds about 25 cm H2O. De-priming means that air is pulled into the nozzles and into the headland/standpipe of the printhead. Air in this region can lead to printhead failures (ranging from a few nozzles out to all nozzles out). De-prime failures caused by excessive back pressure at the nozzle can occur during initial setup, cleaning of the printhead, or any time the end user handles the bulk ink supply system. De-prime failure is the primary reason cited by users for returning bulk ink supply systems for refund/exchange.
Competing with the need to limit excessive back pressure at the printhead for proper printing operation, is the need to maintain sufficient back pressure to prevent unintended discharge of ink from the nozzles of a printhead (ink drool). Specifically, as the back pressure at the printhead approaches 0 cm H2O, the capillary forces drawing the ink overcome the back pressure force and ink drool occurs. Ink drool is a common problem in bulk ink supply systems, but does not cause functional failures. Ink drool caused by insufficient back pressure at the nozzle can occur during initial setup, cleaning of the printhead, or any time the end user handles the bulk ink supply system, where the positioning level of the printhead approaches that of the reservoir. Thus, when properly controlled, back pressure substantially prevents ink drool from a printhead and acts to draw ink from an ink supply.
One prior art attempt to address printhead de-prime problems can be found in U.S. Pat. No. 6,172,694 (Droege et al.), which utilizes a flapper-type gate valve.
Thus, a need exists for a check valve for use in a bulk ink supply system, which better controls the back pressure at the printhead and thereby reduces the occurrence of de-priming of the printhead.
The present invention is directed to a ball check valve for use in a bulk ink supply system of an inkjet printing system, for disposal in an ink flow path between an ink reservoir and a printhead, so as to control back pressure at the printhead thereby reducing the occurrence of de-priming of the printhead, comprising: a valve body defining a chamber with an inlet and an outlet; a ball disposed in the chamber, the ball having a diameter; a ball retainer disposed in the inlet, the ball retainer having an aperture with a diameter which is less than the diameter of the ball, wherein backflow of ink in the chamber causes the ball to seat against the ball retainer, placing the ball check valve in a closed position such that ink flow through the aperture is restricted.
According to another embodiment of the present invention, a bulk ink supply system for supplying ink to an inkjet printer comprises: an ink reservoir; a printhead in fluid communication with the ink reservoir; an ink flow path between the ink reservoir and the printhead; and a ball check valve disposed in the ink flow path, wherein the ball check valve is adapted to control back pressure at the printhead thereby reducing the occurrence of de-priming of the printhead.
A further embodiment of the present invention is a method of controlling back pressure at a printhead in a bulk ink supply system thereby reducing the occurrence of de-priming of a printhead, comprising the steps of: disposing a ball check valve in an ink flow path between the printhead and an ink reservoir; and placing the ball check valve in a closed position when backflow of ink in the ball check valve occurs.
A yet further embodiment of the present invention is a method of making a ball check valve adapted to control back pressure in a bulk ink supply system, thereby reducing the occurrence of de-priming of a printhead, the bulk ink supply system having an ink reservoir, a printhead in fluid communication with the ink reservoir via an ink flow path, and an interconnector disposed in the ink flow path between the printhead and the ink reservoir, comprising the steps of: disposing a ball within the interconnector; and disposing a ball retainer within the interconnector, wherein the ball retainer has an aperture and a valve seat for sealably engaging the ball such that backflow of ink in the ball check valve causes the ball to seat against the valve seat, placing the ball check valve in a closed position such that ink flow through the aperture is restricted.